The structure of a three-cylinder two-stage variable-capacity compressor in a related art is shown in FIG. 1 and FIG. 2, wherein a variable-capacity switching mode of the compressor is: the pressure at a tail of a pin 2′ in the variable-capacity cylinder 1′ is always a low pressure, and the pressure in a seal cavity (that is, a head of the pin 2′) at a tail of a variable-capacity cylinder sliding vane groove 3′ is a high pressure or a low pressure. When the tail of the variable-capacity cylinder sliding vane groove 3′ is connected with the low pressure, a pressure of the head of the pin 2′ is equal to a pressure of the tail of the pin 2′, the pin 2′ moves upward under an elastic force of a spring 4′, and engages a sliding vane 5′, the sliding vane 5′ is locked, the variable-capacity cylinder 1′ is unloaded, and at this time, the compressor is operated in two cylinders. When the tail of the variable-capacity cylinder sliding vane groove 3′ is communicated with the high pressure, a pressure difference is formed between the head of the pin 2′ and the tail of the pin 2′, the pin 2′ moves downward against the elastic force of the spring 4′, the pin 2′ is disengaged from the sliding vane 5′, the sliding vane 5′ can normally move, the variable-capacity cylinder 1′ works, and at this time, the compressor is operated in three cylinders.
When the three-cylinder two-stage variable-capacity compressor adopts the above variable-capacity switching mode, an internal pressure of the variable-capacity cylinder 1′ after unloaded is a low pressure, an internal pressure of a housing 6′ is a high pressure, the pressure difference between an inside and outside of the variable-capacity cylinder 1′ is large, refrigeration oil will enter into the variable-capacity cylinder 1′ through a clearance between a lubrication passage of a crankshaft and a cylinder roller, and thus the refrigeration oil will be accumulated in the variable-capacity cylinder 1′. Therefore, when the compressor operation mode is switched from two-cylinder operation to three-cylinder operation, the variable-capacity cylinder 1′ will compress the refrigeration oil. However, because the refrigeration oil is incompressible, the load of the compressor may suddenly increase, even causing over-current protection of a controller to result in shutdown, so there is a certain degree of reliability risk.